1. Field of the Invention
The present invention relates to a torque distribution control device disposed between laterally opposed vehicle wheels for controlling distribution of engine torque to the wheels independently.
2. Description of the Prior Art
An example of a prior art torque distribution control device is disclosed in Japanese Patent Provisional Publication Nos. 62-94421 and 62-181915.
The Japanese Patent Provisional Publication No. 62-94421 discloses two multi-disk clutches incorporated in a vehicle drive line for controlling distribution of engine torque to laterally opposed vehicle wheels independently. The multi-disk clutches are adapted to increase distribution of engine torque, upon low-to-middle speed turning, to the outer wheel for thereby improving the turning ability and, upon high-speed turning, to the inner wheel for thereby improving the turning stability.
The Japanese Patent Provisional Publication No. 62-181915 discloses two hydraulic clutches incorporated in a longitudinal vehicle drive line for controlling distribution of engine torque to laterally opposed rear wheels independently. Japanese Patent Provisional Publication No. 62-181916 discloses to control, by utilizing a similar arrangement, distribution of engine torque to laterally opposed vehicle wheels in response to a vehicle speed and steering angle, particularly with a view to preventing a spin of the more lightly loaded one of the wheels. Japanese Patent Provisional Publication No. 62-181917 discloses to control, by utilizing a similar arrangement, distribution of engine torque to laterally opposed vehicle wheels in response to a steering angle and lateral acceleration with a view to improving the turning ability and stability.
The above described prior art torque distribution control devices encounter the following problems.
(1) The clutches utilized in the prior art devices do not allow, when supplied with a high hydraulic fluid pressure and put into complete engagement, any relative rotation between input and output members. Due to this, it is necessitated, upon turning, to reduce the torque transmitted to the inner wheel for thereby producing a rotational speed differential between the laterally opposed vehicle wheels, resulting in the total amount of the torque transmitted to the laterally opposed pair of driving wheels being reduced and therefore the driveability at turning is deteriorated.
(2) The prior art control disclosed by Japanese Patent Provisional Publication No. 62-94421 is adapted to make a difference in torque distribution between laterally opposed vehicle wheels upon turning. Due to this, an improved turning ability and turning stability in response to a road surface condition, accelerating operation, etc. cannot always be attained. For example, a tendency to a strong oversteer is caused upon low-to-middle speed turning or a tendency to a strong understeer is caused upon high-speed turning.
The prior art control disclosed by Japanese Patent Provisional Publication No. 62-181916 has a tendency of causing, when executed in such a manner that the torque distribution conforms to the load distribution, a strong oversseer upon highly laterally accelerated turning in which the load on the inner wheel is reduced rapidly.
Further, the prior art control disclosed by Japanese Patent Provisional Publication No. 62-181917 has a tendency of causing, when executed so as to reduce the torque distribution to the laterally accelerated outer wheel, a strong understeer upon high-speed turning.
(3) A hydraulic pressure source, accumulator and actuator including a control valve, etc. are necessitated, resulting in the devices being large-sized and heavy.